Th.--Sci. nat.--Lille 1, 1979. N°: 458. / Contient des articles.

Th.--Sci. nat.--Nancy--I.N.P.L., 1977.

abstract: Membrane protein structure is continuing to be a topic of interest across the scientific community. However, high resolution structural data of these proteins is difficult to obtain. The amino acid transport protein, Outer Envelope Protein, 16kDa (OEP16) is a transmembrane protein channel that allows the passive diffusion of amino acids across the outer chloroplast membrane, and is used as a model protein in order to establish methods that ultimately reveal structural details about membrane proteins using nuclear magnetic resonance (NMR) spectroscopy. Methods include recombinant expression of isotope enriched inclusion bodies, purification and reconstitution in detergent micelles, and pre-characterization techniques including circular dichroism (CD) spectroscopy, dynamic light scattering (DLS), and high pressure liquid chromatography (HPLC). High resolution NMR spectroscopy was able to assign 99% of the amide backbone and the chemical shifts provided detailed secondary structure of OEP16 on a per residue basis using the software TALOS+. Relaxation studies explored the intramolecular dynamics of OEP16 and results strongly support the resonance assignments. Successful titration studies were able to locate residues important for amino acid binding for import into the chloroplast as well as provide information on how the transmembrane helices of OEP16 are packed together. For the first time there is experimental evidence that can assign the location of secondary structure in OEP16 and creates a foundation for a future three dimensional structure. / Dissertation/Thesis / Ph.D. Biochemistry 2012

The theoretical description of multicomponent transport across nonporous polymeric membranes was investigated using two alternative frameworks; the phenomenological approach of irreversible thermodynamics and the mechanistic Stefan-Maxwell formulation. The transport models developed account for potential equilibrium and/or kinetic coupling of fluxes and the contribution of diffusion induced non-selective flow within the polymer. Transient measurements coupled with transient models enable a more detailed evaluation of the complex multicomponent transport phenomena occurring within the nonporous polymer. The models developed in this study were validated against transient dialysis and pervaporation data for (ethanol-water)/silicone rubber system. A critical assessment was obtained by recovering the model parameters from the dialysis data and using the same parameters to predict the transient pervaporation performance. Separate evaluation of the equilibrium and kinetic contributions requires a thermodynamic model to describe the non-ideality of the polymer solution. The uptake of small polar solutes by hydrophobic polymers is not well described by the classical Flory-Huggins model. An empirical modification was developed which retains the basic form of the Flory-Huggins model but allows the interaction parameters to be a simple function of activity. This modification provided a physically realistic description of the sorption equilibria for the {ethanol- water}/silicone rubber system over conditions ranging from a low pressure vapour to a saturated liquid. The phenomenological approach of irreversible thermodynamics was used to develop transient models of dialysis and pervaporation. The numerical solution of the model equations, which constitute a set of coupled partial differential equations, was accomplished by the application of the method of lines. Average phenomenological diffusion coefficients recovered from dialysis data can give a good qualitative prediction of pervaporation performance provided the diffusion coefficients satisfy the Onsagar reciprocal relationships. However, a quantitative prediction requires the explicit inclusion of the concentration dependence of the diffusivities, which is best achieved within the mechanistic Stefan-Maxwell formulation. A generic model of membrane transport was formulated using the mechanistic Stephan-Maxwell approach and generalised driving forces, which included the contribution from the various internal and external driving forces. Transient models of dialysis and pervaporation were developed which used exactly the same generic model to describe the transport through the membrane. A notable advantage of the generic model lies in the fact that the Stephan-Maxwell diffusivities retain their physical significance irrespective of the number of components present. This offers the opportunity of recovering many of the model parameters from relatively simple binary experiments. The results obtained indicate that the generic model is capable of describing the transient dialysis and pervaporation of the {ethanol-water}/silicone rubber system with an identical set of concentration dependent equilibrium and diffusive parameters. The generic model provides a solid framework for the theoretical description of diverse processes employing a nonporous polymer as the selective separation barrier.

A Twyman-Green interferometer was used to study the selective transport of ethanol-water mixtures of various concentration across a nonporous homogeneous silicone rubber membrane at 25°C. The instrument developed enabled the measurement of the transient concentration profiles within the boundary layers bathing the membrane. Measurements as close as 5um from the membrane surface were possible. The majority of the reported interferometric studies of liquid/membrane transport have been limited to the observation of the fringes and stop short of a full theoretical analysis. Such analysis is complicated by the optical effects of light deflection and the computational burden involved in the transient solution of the mathematical models required to describe membrane transport. A rigorous treatment of light deflection was developed on the basis of Fermat's principle of least time. The transient numerical solution of the model equations was accomplished by the application of the method of lines. To decouple the equilibrium and kinetic phenomena in membrane transport requires the independent measurement of the sorption isotherm. Traditional techniques for measuring the extent and composition of the imbibed phase involve removing the membrane from the liquid and are therefore limited by the inherent difficulties of obtaining a 'clean' separation. This was circumvented by measuring the excess (relative) sorption isotherm without removing the membrane from the liquid. The data was analysed in terms of Flory-Huggins thermodynamics which was fitted to the measured excess isotherm across the entire concentration range. For a binary mixture, transport across a homogeneous membrane involves two simultaneous fluxes which can be coupled through kinetic and/or equilibrium interactions. A measure of the extent of coupling was obtained by comparing the results from a simplified 'decoupled' flux model with those based on a 'coupled' flux model allowing for equilibrium interactions. Such interactions were found to have little effect on the flux of ethanol but strongly influenced the flux of water across silicone rubber. In particular, coupling through equilibrium interaction was found to be responsible for as much as 75% of the total flux of water. The diffusion coefficients of both ethanol and water in silicone rubber were shown to decrease strongly with alcohol concentration.

Regulation at the post-transcriptional level is gaining significance at a rapid pace. One example is the storage of messenger mRNA molecules in a translationally quiescent state, the so-called "masked messengers". Their existence has been known since the 1960s, but many details of their composition and structure have not yet been resolved. Masked messenger RNAs are particularly abundant in the oocytes of the African clawed toad Xenopus laevis. The aim of this study has been to examine the proteins bound to stored mRNAs in the oocytes, by focussing on the Y-box proteins which had already been identified as major components in mRNA masking, and by analyzing some of the other unidentified mRNP proteins. The YB proteins were studied in greater detail, gaining fresh information about their RNA-binding properties, defining distinct binding domains. The presence of an mRNP-associated protein kinase was confirmed, and binding assays suggested that phosphorylation influences the ability of the YB proteins to bind to mRNA. cDNA expression libraries were screened both with an RNA-binding assay and with an immunoscreening method, isolating a variety of known and novel cDNAs. Peptide sequencing of mRNP proteins revealed the presence of an RNA helicase distinct from the translation initiation factor eIF4A. It is postulated that the RNA helicase, in addition to the YB proteins, will be seen to have an important role in the formation and activity of the masked messenger RNA particles.

No description available.

No description available.

Membrane surface modification is often utilized to combat membrane fouling, i.e., the deterioration of membrane performance with time. Among many modification methods, the effect of coating the surface of a commercial membrane with electrospun nanofibers on the membrane performance has received little attention. In this work, a commercial polyethersulfone (PES) ultrafiltration membrane was modified by electrospinning PVDF hydrophobic nanofibers for different time periods, i.e., 25min, 125min, and 250min, and its effect on the filtration performance was investigated. It was found that coating with the electrospun nanofiber layer enhanced the pure water permeation (PWP) flux. While the fouling of electrospun PES (EPES) membranes was more severe when they filtered Ottawa River (OR) Water or protein solutions, their final flux was still higher than that of the PES membrane. The membranes were further characterized by scanning electron microscopy (SEM), contact angle measurement and pore size and pore size distribution. The relationship between these characteristics and the membrane performance was discussed.

Orientadores: Teresa Massako Kakuta Ravagnani, Leila Peres / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-18T23:18:07Z (GMT). No. of bitstreams: 1 Araujo_PauloJardelPereira_D.pdf: 15740528 bytes, checksum: bd5969744efcacfde55b69c10f951f33 (MD5) Previous issue date: 2011 / Resumo: O biodiesel além de ser biodegradável e obtido de fontes renováveis, apresenta propriedades físico-químicas muito semelhantes ao diesel de petróleo, não necessitando de um novo motor para utilização do mesmo. A rota química mais comumente usada para obtenção do biodiesel é a transesterificação. Nesta, pela reação de um álcool com os triacilgliceróis (TAG) presentes principalmente em óleos vegetais e gordura animal, são produzidos o biodiesel e, como produto secundário, o glicerol em grandes quantidades. A presença deste glicerol é indesejada, pois além de diminuir a produtividade do biodiesel pelo equilíbrio termodinâmico estabelecido no processo, também aumenta seu custo pelo alto tempo de decantação e/ou uso de centrífugas para remover o glicerol do biodiesel. Devido a este inconveniente, o presente trabalho propõe rota alternativa para separação do glicerol, utilizando membrana de microfiltração (TiO2/Al2O3). Vários sistemas foram analisados, focando a separação do glicerol, o aumento do fluxo permeado e da conversão de TAG na catálise heterogênea. Inicialmente estudou-se a permeabilidade e seletividade dos reagentes e produtos obtidos na síntese do biodiesel com a membrana, através de experimentos binários. A partir destes resultados, estabeleceu-se uma nova configuração do sistema para então analisar estes fatores em misturas compostas pelos quatro constituintes do processo através de um planejamento fatorial. Os resultados apresentados geraram modelos que descrevem com 95% de confiabilidade o coeficiente de rejeição ao glicerol e o fluxo permeado frente aos fatores analisados (nível de emulsificação, razão molar óleo/etanol e conversão de TAG). Selecionou-se então, uma melhor faixa destes fatores que resultem em um máximo de rejeição ao glicerol com máximo fluxo permeado, obtendo um resultado bastante representativo do processo que apresentou um bom fluxo permeado (90,11kg/h.m2) com alta rejeição de glicerol (98,69%). Posteriormente propôs-se um estudo do processo simultâneo de reação e separação (leito fixo catalítico envolto em membrana), sendo selecionado para a reação de síntese um catalisador heterogêneo (SrO suportado em alumina), visando facilitar o processo de separação e reduzir significativamente o número de etapas de purificação dos produtos. Os resultados de conversão do TAG foram baixos, impossibilitando uma análise completa do sistema com esta configuração do ponto de vista de reação e separação concomitante / Abstract: In addition to being biodegradable and renewable, Biodiesel presents physicochemical properties very similar to those of petroleum-based diesel, so a new engine is not required for its use. The most commonly used chemical process for obtaining biodiesel is transesterification. In this process, through the reaction of an alcohol with triacylglycerols (TAG) present mainly in vegetable oils and animal fat, biodiesel is formed with large quantities of glycerol as a byproduct. The presence of glycerol is unwanted because besides reducing the productivity of biodiesel through the thermodynamic equilibrium established in the process, it also increases the cost due to the long time for settling and/or use of centrifuges for removing the glycerol from biodiesel. Taking into account this inconvenience, this paper proposes an alternative process for the separation of glycerol, using TiO2/Al2O3 membranes. Various systems were analyzed, focusing on the separation of glycerol, the increase of the permeate flux, and the increase in the TAG productivity in heterogeneous catalysis. At first we studied the permeability and selectivity of reagents and products obtained in the biodiesel synthesis with a membrane through binary experiments. From these results a new configuration of the system was established, with subsequent analysis of the new interaction in mixtures of the four components of the process (oil, Ethanol, Biodiesel, glycerol) using a factorial design as tool. Results presented in the factorial design generated models that describe with 95% reliability the glycerol rejection coefficient and the permeate flux compared to the analyzed factors (level of emulsification, molar ratio of oil/ethanol and TAG conversion). A best range of factors that result in a maximum glycerol rejection with maximum permeate flux was selected, obtaining a fairly representative result of the process showing a good permeate flux (90.11 kg/h.m2) with high glycerol rejection rate (98.69%). Subsequently, the study of the reaction and separation simultaneous process was proposed (fixed catalytic bed involved in a membrane) selecting an heterogeneous catalyst (SrO on alumina) to facilitate the separation process and significantly reduce the number of purification steps of products. Results of biodiesel conversion were low, preventing a full assessment of the system with this configuration considering simultaneous reaction and separation / Doutorado / Sistema de Processos Quimicos e Informatica / Doutor em Engenharia Química